Remove unnecessary nullable types in examples.

[ksokolovskyi]

Description

• Removes unnecessary bool? usage in examples

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• I followed the breaking change policy and added Data Driven Fixes where supported.
• All existing and new tests are passing.

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests or get an explicit test exemption before merging.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing. If you believe this PR qualifies for a test exemption, contact "@test-exemption-reviewer" in the #hackers channel in Discord (don't just cc them here, they won't see it!). The test exemption team is a small volunteer group, so all reviewers should feel empowered to ask for tests, without delegating that responsibility entirely to the test exemption group.

[gemini-code-assist]

Code Review

This pull request correctly removes unnecessary nullable types from onChanged callbacks in several examples, which improves code clarity and aligns with best practices. I've found one area where the implementation can be further improved for better readability and adherence to idiomatic Dart/Flutter code.

[stuartmorgan-g]

test-exempt: code refactor with no semantic change

[dkwingsmt]

LGTM! (I'm surprised that these files compile at all)

[ksokolovskyi]

LGTM! (I'm surprised that these files compile at all)

@dkwingsmt, me either. Thanks a lot for the review!

According to the Gemini:

Your code compiles and works because Dart allows a function that accepts a nullable type (e.g., bool?) to be assigned to a parameter that expects a function accepting a non-nullable type (e.g., bool). This is known as covariance in function parameters (or the "Liskov Substitution Principle" applied to functions).